1. Field of the Invention
The present invention relates to a clutch hub used in, for example, a wet-type multiple disc clutch, or the like.
2. Related Background Art
An automatic transmission for a vehicle is generally equipped with a planetary gear transmission mechanism of three to five speed levels, in addition to a torque converter which serves as a fluid coupling, and speed change is conducted by properly locking or releasing a constituent element (such as a sun gear or a planetary gear) of the planetary gear transmission mechanism with a clutch or a brake.
As a clutch or a brake to be installed inside the automatic transmission, a wet-type multiple disc in which friction plates and separator plates are arranged alternately is employed, except in some type of band type brakes. A pressure oil from a transmission control hydraulic circuit is used for pressure fitting (frictional engagement) between the two kinds of plates. A wet-type multiple disc clutch is used in an automatic two-wheeled vehicle as a power connecting and disconnecting clutch since a comparatively great amount of torque can be obtained with a smaller area and a smooth connection can be easily attained with such a clutch.
Incidentally, as disclosed in Japanese Patent Application Laid-Open Nos. 7-133830, 2001-232435 and 5-141446, a clutch hub is formed as a spline with a cylindrical portion which is deformed to have concaved and convexed portions. A plurality clutch plates are engaged with this spline to be movable in the axial direction. Then, clutch plates engaged with a spline of a cylinder member to be movable in the axial direction and the aforementioned clutch plates are arranged alternately.
A wet-type multiple disc clutch using this clutch hub is arranged to, when a piston provided inside the cylinder member is driven and both the clutch plates are brought into frictional engagement, or when the frictional engagement between these clutch plates is released, transmit a torque on the input shaft side to a rotating portion on the driven side through the clutch hub or to intercept this torque transmission.
Oil passages are properly formed on teeth of the spline of the clutch hub, and the clutch hub passes oil which is retained on the rear surfaces of the teeth through the oil passages by centrifugal force generated upon rotation thereof, so as to guide the oil onto frictional engagement surfaces of the clutch plates.
This clutch hub is arranged, as disclosed in Japanese Patent Application Laid-Open Nos. 7-133830, 2001-232435 and 5-141446, to have an oil dam which is formed by pressing at an opening end of the tooth of the spline on which the oil passage is formed or in the vicinity thereof, so as to prevent the oil from flowing to the opening side of the clutch hub so that most of the oil is caused to pass through the oil passage and the frictional engagement surface is effectively lubricated.
However, if the aforementioned oil dam is processed by plastic deformation, the precision of the spline on the outer diameter side of the clutch hub with which a pair of frictional engagement elements such as clutch plates are brought into fitting is generally deteriorated. As a result, the engagement or the release of engagement of the pair of frictional engagement elements such as clutch plates could not be performed smoothly.
Particularly, in the pressing work of the oil dam which is disclosed in Japanese Patent Application Laid-Open No. 7-133830, tooth contours of the spline are deformed when the oil dam is produced which causes troubles with movement of the pair of frictional engagement elements such as clutch plates at the engagement or the release of engagement. As a result, the gear shifting performance could be changed and an idling drag could be increased.